AN IN-VITRO MODEL FOR TOXIN-MEDIATED VASCULAR LEAK SYNDROME - RICIN TOXIN-A CHAIN INCREASES THE PERMEABILITY OF HUMAN ENDOTHELIAL-CELL MONOLAYERS

Vascular leak syndrome (VLS) is the doss-limiting toxicity observed in clinical trials of immunotoxins containing ricin toxin A chain (RTA). RTA itself is thought to cause VLS by damaging vascular endothelial c ells, but the exact mechanism remains unclear, This is partially due t o the paucity of appropriate models. To study VLS, we developed an in vitro model in which human umbilical vein-derived endothelial cells we re first grown to confluence on microporous supports and then cultured under low pressure in the presence or absence of RTA. Endothelial cel l barrier function was assessed by measuring the volume of fluid that passed through each monolayer per unit time. We found that RTA signifi cantly increased monolayer permeability at times and concentrations co nsistent with the onset of VLS in patients treated with RTA-based immu notoxins. Scanning electron microscopy showed that intercellular gaps formed in endothelial monolayers exposed to RTA. Intercellular gap for mation followed endothelial cell death caused by the enzymatic activit y of RTA, We conclude that RTA is directly toxic to endothelial cells in vitro and speculate that this contributes to VLS in vivo. (C) 1997 by The American Society of Hematology.